A millimeter wave or micro-wave unit (high frequency unit) used for a radar system incorporated into a vehicle is composed in such a manner that a circuit board, on which various parts are mounted, and MMIC package (Monolithic Microwave Integrated Circuit) (high frequency IC package) are mounted on a housing chassis.
FIG. 1 is a view showing a structure of a conventional high frequency unit. FIG. 1(A) is a plan view showing an outline of the arrangement, and FIG. 1(B) is a sectional view taken on line B-B in FIG. 1(A).
The circuit board 4 and six high frequency IC packages (MMIC packages) 5 are mounted on the housing chassis 1 via the conductive adhesive 2, 3 which will be referred to as an “adhesive” hereinafter. Other parts such as a connector 25 are mounted on the circuit board 4 and, further, the wave guide 26 is formed in the housing chassis 1. In this way, the high frequency unit 6 is composed. In this case, solder or gold or tin brazing may be used as the adhesive.
Referring to FIG. 2, the structure of the high frequency IC package 5 will be explained as follows. FIG. 2(A) is a sectional side view, and FIG. 2(B) is a bottom view of the high frequency IC package 5 from which the cap 14 has been removed.
On the lower face of the board 7 of the high frequency IC package 5, there are provided wiring patterns 11 connected to the high frequency IC chip 8. On the upper face of the board 7 of the high frequency IC package 5, there are provided wiring patterns 12 connected to an external circuit. The wiring patterns 11 on the lower face are connected to the wiring patterns 12 on the upper face via the via hole 13.
The high frequency IC chip 8 is mounted on the lower face wiring pattern 11 on the board 7. The bypass condensers 9 are mounted on the wiring pattern 11. The bypass condensers 9 are parts for determining a characteristic of the high frequency IC. For example, the bypass condensers 9 are provided for preventing the oscillation of the high frequency IC.
On the lower face of the board 7, there is provided a ground pattern 10. One of the electrodes of the bypass condenser 9 is connected to the ground pattern 10 by means of wire bonding connection 15. The high frequency IC chip 8 and bypass condensers 9 are sealed by the cap 14.
In the above conventional high frequency IC package, the bypass condensers 9 are contained in the cap 14 together with the high frequency IC chip 8. Therefore, it is necessary to conduct MCM mounting (Multi-chip module mounting), which causes difficult technical problems. Further, the package size is increased and the number of the manufacturing processes is increased. Therefore, it is difficult to reduce the manufacturing cost. As a result, it is difficult to reduce the size and cost of a millimeter wave unit in which the above high frequency IC package is used.
It is an object of the present invention to simplify and downsize the structure of a high frequency IC package and that of a high frequency unit in which the high frequency IC package is used.
It is another object of the present invention to reduce the number of the manufacturing processes of the high frequency IC package and that of the high frequency unit in the manufacturing method.